Seat belt (also called safety belt) systems have evolved significantly as these systems have become standard equipment in all different types of cars and other vehicles, and as different designs of seat belts have been provided for both active and passive systems. It has been recognized that in order to provide an effective and comfortable seat belt system, it is very desirable that the seat belt webbing itself have a number of desired characteristics.
Desirable seat belt webbing typically should have good lateral stiffness and good resilience across the width of the webbing in order to avoid "roping" conditions, or folding of the webbing, that could result in malfunctioning of the seat belt system. Comfort to the user of the seat belt is enhanced by the use of a soft edge, yet the webbing must still have good abrasion resistance. Further, it is necessary that the webbing be relatively thin, and have low longitudinal stiffness, in order to provide good winding and lock-up characteristics.
According to the present invention, a woven seat belt webbing is provided which has all of the desirable characteristics set forth above. The good lateral stiffness and resilience across the width of the webbing that is, properties sufficient to avoid "roping" conditions, or other folding of the webbing, that could result in malfunctioning of the seat belt system is achieved by providing both monofilament and multifilament filling yarns. The monofilament yarn is a very rigid yarn and provides excellent fold resistance and good resiliency. However it is important that it not protrude at the edges of the webbing. This is accomplished according to the invention by moving the monofilament and multifilament yarns together as one across the full width of the shed with a pick needle while applying a higher tension to the monofilament yarn than the multifilament yarn.
Comfort to the user is achieved according to the present invention by providing a soft and round edge appearance. A soft and round edge appearance is provided in part by controlling the filling tension of the monofilament yarn, as described above; and by providing a particular catchcord formation along one edge of the webbing. This is also accomplished by providing a smaller warp yarn in the selvedge portions of the webbing and a second, larger, warp yarn in the central portions of the webbing, the first warp yarn having smaller dimensional properties than the second yarn so that a round and soft edge appearance is provided. Typically, single ply warp yarns are provided in the selvedge portions and double ply warp yarns of the same nominal denier or detex in the central portion. This also allows the production of a narrower and thinner webbing with soft edges for a given tensile strength, which is very desirable.
Low longitudinal stiffness, which when combined with the thinner webbing offers good winding and lock-up characteristics, is also provided by the use of the smooth monofilament filling yarn. With the thinner webbing, web storage is also substantially increased.
Despite the round and soft edge appearance, seat belt webbing according to the invention also has good abrasion resistance. Again, the monofilament/multifilament construction provides good abrasion resistance in part as a result of the improved lateral stiffness provided thereby which results in a product with good stability. Utilizing the webbing according to the invention, less edge filamentation, less rippling, and less curvature after many cycles of use, can be expected.
The method of making seat belt webbing according to the invention preferably utilizes a needle loom. The method comprises the following steps: (a) Providing warp yarns in a shed. (b) Weaving filling yarns with the warp yarns, the filling yarns comprising a monofilament yarn and a multifilament yarn, by moving the monofilament and multifilament yarns together as one across the full width of the shed with a pick needle, and by applying a different tension to the monofilament yarn than the multifilament yarn so that the monofilament yarn does not protrude on the edges of the webbing. And, (c) providing stitching along one edge of the webbing to hold the filling yarns in place along that edge. Step (a) is practiced by providing different warps for the selvedge portions than the central portion in the shed so that the webbing has a soft and round appearance. This is preferably accomplished by providing single ply warp yarns in the selvedge portions and double ply warp yarns, with each ply of the same nominal denier and detex as the selvedge yarns, in the central portions. Also, steps (b) and (c) are preferably practiced by knitting two catchcord yarns at the edge portion, using a binder thread and a locking thread as the two catchcord yarns, and by controlling the tension of the locking yarn to assure an even edge and a cushion over the filling yarns, and controlling the tension of the binder yarn to allow the filling yarn to pull itself and the binder yarn from the edge of the webbing.
It is the primary object of the present invention to provide a single layer woven belt with good lateral stiffness and good resilience across its width, low longitudinal stiffness, good abrasion resistance, and a soft round edge appearance, and a method of construction thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.